Magmatectonic Zonation of Italy: A Tool to Understanding Mediterranean Geodynamics

The Mediterranean deformation historyThe present tectonic setting of the Western and Central Mediterranean "wide-rift" system (e.g.Ligurian-Provençal and Tyrrhenian basins) and of the surrounding, outward-verging, Apennine-Maghrebian thrust belt (Fig. 1) results from a long history of deformation characterized by the alternation and/or the overprinting of contractional and extensional tectonic phases.Such a history, developed during the last 35 Ma, started while the Alpine-Betic orogeny was undergoing its final collisional stage (Faccenna et al., 2004).Beginning from Late Cretaceous times, the Alpine Tethys ocean progressively closed with generation of the Alpine orogenic belt, presently exposed in the Alps, northwest Corsica, Calabria and in the Betics (southeast Spain) (Stampfli and Borel, 2004).By the end of the Paleocene (~55 Ma ago), the oceanic and/or ultra-thinned continental Tethyan lithosphere had been completely underthrust beneath the African continental plate.Shortening, however, along the Alpine-Betic belt continued at least to the end of the late Eocene.The Alpine collisional activity occurred together with a localized intra-continental extensional phase, which generated the Cenozoic "narrow-rift" system of eastern and central Europe (Fig. 1) (Ziegler, 1992).With the beginning of the early Oligocene (~35 Ma ago), extension started to dominate again over compression.A regional, east-dipping, extensional fault system developed along the south-westward prolongation of the Central Europe Rift System, along the western border of the Western Mediterranean basin, between Corsica-Sardinia and the Provençal region (Fig. 1).During early Miocene times (from ~22 to ~16 Ma ago), the Corsica-Sardinia block, which belonged to the European continental lithosphere, started to undergo a counter-clockwise rotation around a pivot point situated more or less north of present-day Corsica (star in Fig. 2), which led to the opening of Ligurian-Provençal basin.After a period of tectonic quiescence of a few million years, in middle Miocene times (~13 Ma ago) the extensional process started again to the east of the Corsica-Sardinia block.The Adriatic foreland rotated counter-clockwise giving birth to the progressive opening of the Tyrrhenian basin (Fig. 1a).The extensional process was mainly achieved through easterly-dipping, low-angle, and antithetic, high-angle, normal faulting which produced an extensive stretching and thinning of the crust and mantle lithosphere, with localised areas of mantle unroofing and/or the accretion of new oceanic crust (Fig. 1b).The extensional process progressively migrated eastward and is now active and seismogenic along the axis of peninsular Italy (Lavecchia, 1988;Chiarabba et al., 2005).Both the Ligurian-Provençal and the Tyrrhenian extensional phases were characterized by the development of contemporary coeval and co-axial outward-verging fold-and-thrust structures that nucleated at the outer border of the extended regions (Carminati et al., 1998;Finetti et al., 2001). Magmatic phasesEach of the tectonic phases listed above was characterized by distinctive magmatic activity (Figs. 1, 2 and3).The Late Cretaceous to Paleocene Alpine orogenic phase was substantially amagmatic, accompanied by isolated lamprophyric activity, mainly consisting of dyke swarms situated on both the African and European continental sides of the closing Tethys (Vichi et al., 2005; Stoppa, 2008 and references therein).Known Italian occurrences are located in southern Tuscany (~110-90 Ma), in the south-eastern Alps (Calceranica and Corvara in Badia, 70-68 Ma), in south-eastern Sardinia (Nuraxi Figus 62-60 Ma), in the www.intechopen.com

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